How to use auto trace for performance tuning ?

 Autotrace 

SQL> set autotrace traceonly explain ;

SQL> set serveroutput on

SQL>

SQL>

SQL> select * from test;

Execution Plan

----------------------------------------------------------

Plan hash value: 1357081020

--------------------------------------------------------------------------

| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |

--------------------------------------------------------------------------

|   0 | SELECT STATEMENT  |      |     6 |   240 |     2   (0)| 00:00:01 |

|   1 |  TABLE ACCESS FULL| TEST |     6 |   240 |     2   (0)| 00:00:01 |

--------------------------------------------------------------------------

Note

-----

   - dynamic statistics used: dynamic sampling (level=2)

SQL> set autotrace off

SQL>

SQL>

SQL>

SQL> set autotrace on

SQL>

SQL> select * from test;

        ID NAME

---------- --------------------------------------------------

         1 A

         1 A

         1 A

         1 A

         1 A

         1 A

6 rows selected.

Execution Plan

----------------------------------------------------------

Plan hash value: 1357081020

--------------------------------------------------------------------------

| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |

--------------------------------------------------------------------------

|   0 | SELECT STATEMENT  |      |     6 |   240 |     2   (0)| 00:00:01 |

|   1 |  TABLE ACCESS FULL| TEST |     6 |   240 |     2   (0)| 00:00:01 |

--------------------------------------------------------------------------

Note

-----

   - dynamic statistics used: dynamic sampling (level=2)

Statistics

----------------------------------------------------------

          0  recursive calls

          0  db block gets

          4  consistent gets

          0  physical reads

          0  redo size

        724  bytes sent via SQL*Net to client

        380  bytes received via SQL*Net from client

          2  SQL*Net roundtrips to/from client

          0  sorts (memory)

          0  sorts (disk)

          6  rows processed

SQL>

SQL> set autotrace off